This invention relates to a process and a device for carrying out the process for piecing a yarn at a spinning unit of an open-end friction spinning machine. The spinning unit has two rollers that are drivable in the same rotational direction and are arranged next to one another to form a wedge-shaped gap or slot. A feeding and opening device is provided for the feeding of single fibers to the wedge-shaped gap. A yarn withdrawal device is provided for drawing off the formed yarn or thread in the direction of the extension of the wedge-shaped gap and a suction device is provided for holding the forming yarn in the wedge-shaped gap. For the joining or piecing of the yarn, an already spun end section of the yarn is returned to the wedge-shaped gap and the previously interrupted feeding of the fibers is resumed and the yarn end section withdrawn.
In the case of a known process of the intially mentioned type, disclosed in European Published Application (EPOS) No. 34 427, the end section of the yarn is sucked back into the not opened spinning unit by means of a vacuum and is brought into the range of the wedge-shaped gap and is then transferred to the gap. In this case, a yarn length is furnished that is dimensioned in such a way that the end of the yarn end section is disposed in the area of the feeding point where the fibers are fed. Then the previously interrupted feeding of the fibers is resumed after which the yarn is withdrawn. In this arrangement, the end section of the yarn is located in the wedge-shaped gap of the turning rollers during a certain time period after the switching-on of the feeding mechanism before it is again withdrawn. Thus the end section of the yarn receives an increased twist so that the length portion containing the yarn piecing or connection differs from the remaining length of the yarn. It does not seem possible by means of this process to obtain a yarn piecing that can remain in the finished yarn for further processing.
The invention is based on the objective of providing a process and a device of the initially mentioned type by means of which an improved yarn piecing can be obtained.
This objective is achieved according to the invention by stopping the rollers for the piecing process, by inserting the end section of the yarn into the wedge-shaped gap of the stopped rollers and by subsequently switching on the feeding mechanism for the fibers, and again activating the drive of the rollers and the drive of the yarn withdrawal device. By means of these measures, it is first achieved that the return of the end section of the yarn to the wedge-shaped gap is simpler and more reliable, in which case the returned end section of the yarn is also not overtwisted. Since, when the drive of the rollers is turned back on, these rollers do not suddenly reach their normal speed but reach that speed after a certain starting delay, there is also a certain period of time during which it is possible to carry out a suitable feeding of the fibers and a suitable withdrawal again of the yarn, which further improves the quality of the yarn piecing.
In a useful development of the invention, it is provided that the end of the yarn is returned beyond the area of the feeding point of the fibers and that the yarn withdrawal device is switched on before the feeding of the fibers. This makes it possible to also here provide sufficient time periods in order to carry out the steps of the process in a controlled manner. It is useful that the feeding of the fibers and the restarting of the rollers is initiated approximately simultaneously. Since the fibers reach the wedge-shaped gap only with a certain delay after the feeding mechanism is switched back on, and since the rollers also start with a certain delay, there is good coordination of these steps with this arrangement.
In an advantageous development of the invention, it is also provided that the switching-on of the feeding mechanism is coordinated with the drawing off of the end section of the yarn in such a way that the fed fibers will arrive in the wedge-shaped gap at that point in time when the extreme end of the yarn end section reaches the area of the feeding point. Thus it is possible to largely avoid thick sections in the yarn at the piecing connection.
In a further development of the invention, it is provided that the part of the yarn end section that is returned beyond the length of the wedge-shaped gap is guided in a guide in such a way that the end of the yarn end is not transferred to the wedge-shaped gap until it reaches the area of the feeding point. In this manner, it is insured that the end of the yarn end section does not receive excess twisting and is thus in a condition that is favorable for the piecing operation. In this arrangement, it is especially advantageous that the yarn end section in the area that faces away from the withdrawal direction of the yarn, is guided on a path that is at least approximately identical with the last section of the path of the fed fibers. The end of the yarn end section therefore, before the doubling or twisting into the new yarn, carries out a movement that is essentially identical with the movement of the fed fibers so that an even or smooth yarn piecing is obtained.
In a further development of the invention, it is provided that the feeding mechanism for the fibers is first switched on with an amount of fibers that is decreased in comparison to the normal spinning operational amount and is subsequently increased to the operational amount when the end of the yarn end has passed the feeding point. This also facilitates influencing the shape of the yarn piecing and improving it with respect to quality. For the same purpose, it is also advantageous that the withdrawing of the yarn, during the joining or piecing process, takes place at a speed that is different from the operational yarn withdrawal speed. In order to achieve a connection between the end of the yarn end section and the newly fed fibers that is as intensive as possible, it is advantageous that the end of the yarn end section is worked into a type of tuft or fiber beard before the switching-on of the thread pull-off device. This ensures a very close connection between the newly fed fibers and the tufted end of the yarn.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, an embodiment constructed in accordance with the present invention.